Patent GB-726569-A (GB)
Title: Cathode-ray tube of the lenticular grill variety
IPC: H01J29/80
Filed: 1953-03-06
Abstract: 726,569. Cathode-ray tubes. RADIO CORPORATION OF AMERICA. March 6, 1953 [March 18, 1952], No. 6330/53. Class 39 (1). A cathode-ray tube for use in colour or stereoscopic television comprises a focusing electrode in the vicinity of the target, and an auxiliary electrode for collecting back scattered electrons. The target comprises a multiple pattern of elemental image areas, and the focusing electrode provides an array of converging lenses for directing the beam on to the appropriate image area. The auxiliary electrode at an appropriate potential for collecting back scattered electrons provides an array of diverging lenses but the construction, orientation, and arrangement of these electrodes are so chosen that the beam of electrons does not spread beyond the appropriate image area of the target. In a three-gun colour tube with the phosphors on the target 7, Fig. 1, arranged in lines, the focusing electrode 9 consists of wires lying parallel with the phosphor lines, and the auxiliary electrode 11 consists of wires lying perpendicular to the phosphor lines. The focusing and auxiliary electrodes provide arrays of cylindrical lenses. Either electrode may be next adjacent the target. The arrangement is such that the diverging action of the cylindrical lenses formed by the auxiliary electrode is in the direction of the phosphor lines. The wires of the auxiliary electrode may alternatively be so fine and so closely spaced that the diverging effect is negligible as compared with the widths of the phosphor lines. An electron transparent lightreflecting film 13 constituted, for example, of evaporated aluminium renders the entire target surface of the screen conductive. The phosphor areas may be in the form of dots 7<SP>1</SP>, Fig. 10, the focusing electrode 9' consisting of a metal plate provided with apertures corresponding in shape and arrangement to the phosphor dots, and the auxiliary electrode 11<SP>1</SP> consisting of a fine wire mesh. In this arrangement, the focusing and auxiliary electrodes provide arrays of spherical lenses. In a single-gun colour tube with a " line " target, the focusing electrode may consist of two groups of wires, voltages being applied to successive wires of the two groups to shift the electron beam from one set of phosphor lines to another. As shown, Fig. 8, the groups of wires 46, 47 are stretched between two insulating guides 43, 45, and are attached to two conducting electrodes 48, 49. The wires are hooked to the insulating guides and conducting electrodes. In this system, one of the three colour phosphor sets of lines has a frequency of occurrence twice that of the others. The invention may be applied to a colour pick-up tube with a photosensitive screen either of the photo-emissive variety or of the photoconductive variety. In either case, the photosensitive target surface is backed by a transparent electrode, and a set of parallel colour filter strips. When a photoconductive surface is used, it is preferably an antimony-sulphide selenium layer. The invention may also be applied to a cathode-ray tube for use in stereoscopic television systems. The screen consists of a uniform metallized phosphor layer on a thin transparent support which bears equally spaced filter strips of polarizing material, successive strips operating to polarize incident light in mutually perpendicular directions. The screen is viewed by the observer through spectacles with polarized lenses. French Specification 866,065 and German Specification 736,575 are .referred to.